The present invention relates to a method of controlling a seat belt retractor having a function of winding up a seat belt under the power of a motor.
Vehicles are equipped with seat belt retractors in order to ensure the safety of a vehicle occupant upon an accident, such as vehicle collision, and various types of seat belt retractors have been developed. An example of one of the simplest structure among them is shown in FIG. 10.
FIG. 10 discloses a spring cover 41, as a supporting member at one side of the seat belt retractor, is provided with a bearing 41a arranged therein, into which a shaft 42a of a spool 42 is fitted so as to rotate while a biasing force of a spring is applied to the shaft 42a in the winding direction. Around the spool 42, a seat belt is wound.
Inside the spool 42, a concave fitted portion is formed, into which one end of a torsion bar 43 is fitted. The other end of the torsion bar 43 is fitted into a concave fitted portion formed In a locking base 44. A shaft 44a of the locking base 44 penetrates a hole 45a of a lock gear 45 so as to fit into a bearing of a retainer 46, as another supporting member at the other side of the seat belt retractor.
According to the aforementioned mechanism, as a result, the spool 42 is supported at its rotating axis by the spring cover 41 and the retainer 46 and is rotated to wind up the seat belt by means of the biasing force of the spring. The spring cover 41 and the retainer 46 are fixed at both sides of a base frame 48, so that the spool 42 is accommodated within the base frame 48.
Among these components, the locking base 44 and the lock gear 45 are relatively rotatable by a predetermined angle. The lock gear 45 is biased by a spring 49 relative to the locking base 44 in the seat belt withdrawing direction to the limit of the relative rotation.
When the seat belt is withdrawn in a normal state, since there is no resistance against the rotation of the lock gear 45, the lock gear 45 can not overcome the biasing force of the spring 49 to thereby rotate together with the locking base 44.
Even when the spool 42 is rotated by the spring force so as to rotate the locking base 44 in the winding direction, the lock gear 45 rotates together with the locking base 44 because the lock gear 45 is originally biased to the limit of the rotation relative to the locking base 44 in this direction as mentioned above.
When the seat belt is rapidly withdrawn due to a collision or the like, a flywheel 50 accommodated within the lock gear 45 is displaced by overcoming the biasing force of a spring 51, thereby preventing the relative rotation of the lock gear 45 relative to the retainer 46 and stopping the rotation of the lock gear 45.
Then, the locking base 44 rotates relative to the lock gear 45 against the biasing force of the spring 49. A mechanism is constructed such that a pawl 52 accommodated in the locking base 44 protrudes outside by this relative rotation, and a gear of the externally protruded pawl 52 engages a toothed portion 48a formed in the base frame 48, thereby stopping the rotation of the locking base 44 too. This mechanism is called “locking mechanism”.
Accordingly, the rotation of the torsion bar 43 is also stopped and the spool 42 is allowed to rotate only by an angle corresponding to a twist of the torsion bar 43.
Therefore, the seat belt is thereafter withdrawn under a tension generated by the twist of the torsion bar. This mechanism is called “force limiter”.
The above is a general description of the seat belt retractor. The seat belt retractor includes complex mechanisms for use as a mechanism for stopping rotation of the lock gear 45 by the movement of the flywheel 50 and a mechanism for protruding the pawl 52 outside. However, the seat belt retractor is well known in the art and is used in common, so that more detailed description may be omitted.
The, the seat belt retractor shown in FIG. 10 is also provided with a seat belt winding-up mechanism called as a pyrotechnic pretensioner. This is for rapidly and strongly winding up the seat belt when a vehicle collision actually takes place, thereby restraining the occupant to the vehicle seat. Hereinafter, the structure of the pyrotechnic pretensioner will be explained.
The pretensioner comprises a pretensioner cover 61, a pretensioner plate 62, and a pipe 63 between the pretensioner cover 61 and the pretensioner plate 62. Disposed at one end of the pipe 63 is a gas generator 64. Inside the pipe 63, a stopper spring 65, a piston 66, and a plurality of balls 67 are arranged. The pipe 63 has a cut-out portion formed in a portion near the other end thereof and a guide block 68 inserted in the other end.
The pretensioner cover 61 is provided with two pins 69. A ring gear 70 is received and supported by the pins 69. The front most ball 67 is sandwiched and fixed between external teeth of the ring gear 70 and an inwardly facing wall of the pipe 63 where no cut-out exists.
On the other hand, the pinion 72 is fitted around the gear 71 of the spool 42. In the normal state, the ring gear 70 and the pinion 72 are out of mesh. When gas is generated from the gas generator 64, the balls 67 are pressed via the piston 66 by the pressure of generated gas so as to break the pins 69, whereby the ring gear 70 becomes free and meshes the pinion 72. In this state, the external teeth 71a of the ring gear 70 are pressed by the balls 67 to rotate the ring gear 70. Accordingly, the ring gear 70 rotates the spool 42 via the pinion 72. In this manner, the seat belt is pretensioned. The mechanism as described above is also well known in the art so that the more detailed description will be omitted.